Field
The embodiments described below relate to the measurement of biometric data. Some embodiments relate to photoplethysmographic sensors.
Description
Recent consumer interest in personal health has led to a variety of personal health monitoring devices being offered on the market. Such devices, until recently, tended to be complicated to use and were typically designed for use with one activity, e.g., bicycle trip computers.
Recently, personal health monitoring devices (also referred to herein as “biometric tracking” or “biometric monitoring” devices) have expanded to track multiple metrics of the wearer. For example, Fitbit, Inc. produces a number of biometric tracking devices that can have a number of features and elements, such as displays, batteries, sensors, wireless communications capabilities, power sources, and interface buttons, as well as mechanisms for attaching these devices to a pocket or other portion of clothing or to a body part of the wearer, packaged within a small volume which are configured to track, among other things, steps, distance, calorie expenditure, active minutes, elevation (e.g., as measured in floors or stairs), speed, pace, and the like.
To track these metrics, these devices may collect, process and display a large variety of data using a variety of sensors. One type of sensor used in some biometric tracking devices is a heart rate sensor. These heart rate sensors typically operate by emitting light into the skin of the user and then measuring the light reflected or diffused back after the emitted light interacts with the user's skin.